Symbiotic Dinoflagellate Symbiodinium Research Articles

Structures and organizations of PSI–AcpPCI supercomplexes from red tidal and coral symbiotic photosynthetic dinoflagellates

Marine photosynthetic dinoflagellates are a group of successful phytoplankton that can form red tides in the ocean and also symbiosis with corals. These features are closely related to the photosynthetic properties of dinoflagellates. We report here three structures of photosystem I (PSI)-chlorophylls (Chls) a/c-peridinin protein complex (PSI-AcpPCI) from two species of dinoflagellates by single-particle cryoelectron microscopy. The crucial PsaA/B subunits of a red tidal dinoflagellate Amphidinium carterae are remarkably smaller and hence losing over 20 pigment-binding sites, whereas its PsaD/F/I/J/L/M/R subunits are larger and coordinate some additional pigment sites compared to other eukaryotic photosynthetic organisms, which may compensate for the smaller PsaA/B subunits. Similar modifications are observed in a coral symbiotic dinoflagellate Symbiodinium species, where two additional core proteins and fewer AcpPCIs are identified in the PSI-AcpPCI supercomplex. The antenna proteins AcpPCIs in dinoflagellates developed some loops and pigment sites as a result to accommodate the changed PSI core, therefore the structures of PSI-AcpPCI supercomplex of dinoflagellates reveal an unusual protein assembly pattern. A huge pigment network comprising Chls a and c and various carotenoids is revealed from the structural analysis, which provides the basis for our deeper understanding of the energy transfer and dissipation within the PSI-AcpPCI supercomplex, as well as the evolution of photosynthetic organisms.

Temperature regulates the recognition activities of a galectin to pathogen and symbiont in the scleractinian coral Pocillopora damicornis

Lectins serve as essential pattern recognition receptors, and play important roles in the recognition of non-self and mediation of innate immune response in metazoans. Scleractinian corals are vulnerable to pathogen infection and endosymbiosis disruption under heat stress that can finally lead to coral bleaching. In this study, a cDNA sequence encoding one galectin was cloned in scleractinian coral Pocillopora damicornis (PdGLT-1). The deduced PdGLT-1 protein shared highest amino acid sequence similarity (99%) with galectin from Stylophora pistillata (XP_022806650.1), and was composed of one signal peptide, one Collagen domain and one Gal-Lectin domain. PdGLT-1 recombinant protein (rPdGLT-1) was expressed and purified in vitro. Binding activities of rPdGLT-1 to bacteria and symbiont were determined using western blotting method. Results showed that rPdGLT-1 was able to bind to gram-positive bacterium Streptococcus mutans, gram-negative bacteria Vibrio coralliilyticus and Escherichia coli, with the highest activity for V. coralliilyticus, and further agglutinated them. The bound rPdGLT-1 to Symbiodinium (10-104 cells mL−1) was detectable, and its binding ability was concentration-dependent. Furthermore, dual binding activities were determined under different temperatures (20, 25, 30 and 35 °C), and the optimal temperatures were found to be 25 and 30 °C for V. coralliilyticus and Symbiodinium, respectively. Results suggested that PdGLT-1 could recognize pathogenic bacteria and symbiotic dinoflagellates Symbiodinium. However, their recognition activities were repressed under high temperature (>30 °C). This study provided insights into the underlying mechanism of lectin modulation to heat bleaching through its pathogen and Symbiodinium recognition in the scleractinian coral P. damicornis.

Isolation and characterization of a tandem-repeated cysteine protease from the symbiotic dinoflagellate Symbiodinium sp. KB8.

A cysteine protease belonging to peptidase C1A superfamily from the eukaryotic, symbiotic dinoflagellate, Symbiodinium sp. strain KB8, was characterized. The protease was purified to near homogeneity (566-fold) by (NH4)2SO4 fractionation, ultrafiltration, and column chromatography using a fluorescent peptide, butyloxycarbonyl-Val-Leu-Lys-4-methylcoumaryl-7-amide (Boc-VLK-MCA), as a substrate for assay purposes. The enzyme was termed VLKP (VLK protease), and its activity was strongly inhibited by cysteine protease inhibitors and activated by reducing agents. Based on the results for the amino acid sequence determined by liquid chromatography–coupled tandem mass spectrometry, a cDNA encoding VLKP was synthesized. VLKP was classified into the peptidase C1A superfamily of cysteine proteases (C1AP). The predicted amino acid sequence of VLKP indicated a tandem array of highly conserved precursors of C1AP with a molecular mass of approximately 71 kDa. The results of gel-filtration chromatography and SDS-PAGE suggested that VLKP exists as a monomer of 31–32 kDa, indicating that the tandem array is likely divided into two mass-equivalent halves that undergo equivalent posttranslational modifications. The VLKP precursor contains an inhibitor prodomain that might become activated after acidic autoprocessing at approximately pH 4. Both purified and recombinant VLKPs had a similar substrate specificity and kinetic parameters for common C1AP substrates. Most C1APs reside in acidic organelles such as the vacuole and lysosomes, and indeed VLKP was most active at pH 4.5. Since VLKP exhibited maximum activity during the late logarithmic growth phase, these attributes suggest that, VLKP is involved in the metabolism of proteins in acidic organelles.

Symbiodinolactone A, a new 12-membered macrolide from symbiotic marine dinoflagellate Symbiodinium sp.

A new 12-membered macrolide, symbiodinolactone A, was isolated from the culture broth of symbiotic marine dinoflagellate Symbiodinium sp. The gross structure of symbiodinolactone A was elucidated by spectroscopic analyses, and the relative configuration was elucidated by the J-based configuration analysis and density-functional theory calculations. Symbiodinolactone A is the new 12-membered macrolide possessing an E double bond between C-4 and C-5, a branched methyl group at C-7, and a 1,2,3-trihydroxybutyl group at C-11. Symbiodinolactone A is the first usual size macrolide and the first non-nitrogen-containing macrolide from dinoflagellate Symbiodinium sp. Symbiodinolactone A might be generated by the unexplained dinoflagellate polyketide biosynthetic machinery.

Short-term effects of heavy metal and temperature stresses on the photophysiology of Symbiodinium isolated from the coral Fungia repanda

Abstract. Ghoora MD, Pilly SS, Chumun PK, Jawaheer S, Bhagooli R. 2018. Short-term effects of heavy metal and temperature stresses on the photo-physiology of Symbiodinium isolated from the coral Fungia repanda. Ocean Life 2: 11-20. This study aimed to investigate the effects of the heavy metals, copper, zinc and lead, on the photo-physiology of the symbiotic dinoflagellate Symbiodinium isolated from the coral Fungia repanda. Freshly isolated Symbiodinium found to belong to clade C were exposed to different concentrations of the three heavy metals for 3-hour and 18-hour treatments at 28°C and 32°C. The Pulse Amplitude Modulated (PAM) fluorometry technique was used to determine the maximum quantum yield (Fv/Fm), relative maximum electron transport rate (rETRmax) and maximum non-photochemical quenching (NPQmax) of the photosystem II (PSII). An increase in non-photochemical quenching accompanied by a decrease in photosynthetic capacity was noted for copper at a concentration of 50 µg/L for both temperatures. The Fv/Fm was not significantly affected by the Zn treatments. However, at 28 °C, isolates treated with 100 µg/L Zn for 18 hours showed an increase in non-photochemical quenching accompanied by a decrease in photosynthetic capacity. Pb had the most profound effect on all of the isolates. The Fv/Fm significantly decreased and an increase in NPQmax was noted. The decrease of rETRmax and increase in NPQmax for the heavy metal bioassays under 32 °C were more significant than at 28 °C. This study suggests that Cu (?50 µg/L), Zn (? 100 µg/L) and Pb decrease the photosynthetic capacity of the Symbiodinium isolates from F. repanda especially more so with increasing temperatures.

Genetic diversity of giant clams (Tridacna spp.) and their associated Symbiodinium in the central Red Sea

The biodiversity of the Red Sea remains relatively understudied, particularly for invertebrate taxa. Documenting present patterns of biodiversity is essential for better understanding Red Sea reef ecosystems and how these ecosystems may be impacted by stressors (such as fishing and climate change). Several species of giant clams (genus Tridacna) are reported from the Red Sea, although the majority of research effort has occurred in the Gulf of Aqaba. We investigated the genetic diversity (16S rDNA) of the Tridacna species found in the central Saudi Arabian Red Sea. We also investigated the genetic diversity (ITS rDNA) of symbiotic dinoflagellates Symbiodinium associated with these clams. Samples were collected from nine reefs on a cross-shelf gradient near Thuwal, Saudi Arabia. Two species, T. squamosa and T. maxima, were recorded, with the latter being the most abundant. Tridacna squamosina, a species recently reported in the northern Red Sea, was not found, suggesting that this species is not present or is very rare in our study region. All tridacnids sampled were found to harbor Symbiodinium grouped in Clade A, considered an opportunistic, heat-tolerant symbiont group in anemones and corals. The consistent association with Clade A Symbiodinium in central Red Sea tridacnids may reflect the consequence of adaptation to the relatively extreme conditions of the Red Sea. This study contributes to an ever-growing catalog of Red Sea biodiversity and serves as important baseline information for a region experiencing dynamic pressures.

A diverse host thrombospondin-type-1 repeat protein repertoire promotes symbiont colonization during establishment of cnidarian-dinoflagellate symbiosis.

The mutualistic endosymbiosis between cnidarians and dinoflagellates is mediated by complex inter-partner signaling events, where the host cnidarian innate immune system plays a crucial role in recognition and regulation of symbionts. To date, little is known about the diversity of thrombospondin-type-1 repeat (TSR) domain proteins in basal metazoans or their potential role in regulation of cnidarian-dinoflagellate mutualisms. We reveal a large and diverse repertoire of TSR proteins in seven anthozoan species, and show that in the model sea anemone Aiptasia pallida the TSR domain promotes colonization of the host by the symbiotic dinoflagellate Symbiodinium minutum. Blocking TSR domains led to decreased colonization success, while adding exogenous TSRs resulted in a 'super colonization'. Furthermore, gene expression of TSR proteins was highest at early time-points during symbiosis establishment. Our work characterizes the diversity of cnidarian TSR proteins and provides evidence that these proteins play an important role in the establishment of cnidarian-dinoflagellate symbiosis.

Additive effects of the herbicide glyphosate and elevated temperature on the branched coral Acropora formosa in Nha Trang, Vietnam

The combined effects of the herbicide glyphosate and elevated temperature were studied on the tropical staghorn coral Acropora formosa, in Nha Trang bay, Vietnam. The corals were collected from two different reefs, one close to a polluted fish farm and one in a marine-protected area (MPA). In the laboratory, branches of the corals were exposed to the herbicide glyphosate at ambient (28 °C) and at 3 °C elevated water temperatures (31 °C). Effects of herbicide and elevated temperature were studied on coral bleaching using photography and digital image analysis (new colorimetric method developed here based on grayscale), chlorophyll a analysis, and symbiotic dinoflagellate (Symbiodinium, referred to as zooxanthellae) counts. All corals from the MPA started to bleach in the laboratory before they were exposed to the treatments, indicating that they were very sensitive, as opposed to the corals collected from the more polluted site, which were more tolerant and showed no bleaching response to temperature increase or herbicide alone. However, the combined exposure to the stressors resulted in significant loss of color, proportional to loss in chlorophyll a and zooxanthellae. The difference in sensitivity of the corals collected from the polluted site versus the MPA site could be explained by different symbiont types: the resilient type C3u and the stress-sensitive types C21 and C23, respectively. The additive effect of elevated temperatures and herbicides adds further weight to the notion that the bleaching of coral reefs is accelerated in the presence of multiple stressors. These results suggest that the corals in Nha Trang bay have adapted to the ongoing pollution to become more tolerant to anthropogenic stressors, and that multiple stressors hamper this resilience. The loss of color and decrease of chlorophyll a suggest that bleaching is related to concentration of chloro-pigments. The colorimetric method could be further fine-tuned and used as a precise, non-intrusive tool for monitoring coral bleaching in situ.

UV-A induced delayed development in the larvae of coral Seriatopora caliendrum

Coral reefs are vulnerable to ultraviolet radiation (UVR, 280–400nm). Not only do the fluxes of UVR fluctuate daily, they are also increasing due to global ocean and atmospheric changes. The deleterious effects of UVR on scleractinian corals have been intensively studied, but much less is known about the response of corals in the early pre-settlement phase. In this study, we tested how UVR exposure affects survival and development of Seriatopora caliendrum larvae and examined the photophysiological changes induced in the symbiotic dinoflagellate Symbiodinium. Results showed that the contents of chl c and carotenoids normalized to the number of algae cells in the larvae decreased significantly when larvae were exposed to UVR compared to those protected from UVR, while the cell density of Symbiodinium was higher in UVR-exposed larvae. The effective photochemical efficiency of the symbiotic algae increased when cultured under PAR plus UV-A (here taken as 320–395nm). We further present the novel finding that during the development experiment, presence of UV-A induced a decline in the rates of metamorphosis and settlement, which disappeared when the larvae were also exposed to UV-B (here defined as 295–320nm). However, UVR had no distinguishable effect on the numbers of larvae that either survived, metamorphosed or settled by the end of the culture period. Therefore, it is concluded from this study that UV-A radiation may extend the planktonic duration of coral larvae, but not have an overall inhibitory effect on developmental outcomes.

Embryonic development of the solar-powered nudibranch Phyllodesmium lizardensis (Gastropoda: Nudibranchia)

ABSTRACTIn this pilot study we investigated the early embryonic development of the recently described solar-powered nudibranch species Phyllodesmium lizardensis. In previous studies P. lizardensis has been used as a model system to study the symbiosis between nudibranchs and their symbiotic dinoflagellates Symbiodinium, but the transmission mode of symbionts in the life cycle of this species remained unknown. Embryonic development in P. lizardensis was similar to related nudibranch taxa. Specimens laid clear gelatinous egg masses filled with relatively small egg capsules (81.25 ± 3.78 µm, n = 11). Zygotes developed into planktotrophic veliger larvae that hatched after about 85 hours. No Symbiodinium cells could be detected by means of light microscopy at any developmental stage in zygotes or unhatched veliger larvae. Vertical transmission of symbionts is therefore unlikely; the timing of Symbiodinium acquisition by this species remains unknown.

Different Stress Tolerances of Juveniles of the Coral Acropora tenuis Associated with Clades C1 and D Symbiodinium.

Ikuko Yuyama, Takashi Nakamura, Tomihiko Higuchi, and Michio Hidaka (2016) Reef-building corals are often associated with multiple clades of symbiotic dinoflagellate Symbiodinium spp., where the relative composition of Symbiodinium can alter the phylogenetic properties (e.g., stress responsiveness, growth rate) of the host coral. The genus Symbiodinium contains nine clades, some of which behave differently in response to strong light and/or temperature stresses, for example, clade D Symbiodinium are thermally tolerant. However, previous studies are based on corals present in the field, and it is possible that the corals used in previous experiments did not contain single Symbiodinium clades. For an accurate assessment of the effects of each Symbiodinium clade on host thermal stress resistance, monoclonal cultures of clades C1 and D were inoculated into aposymbiotic juvenile polyps. Photosynthetic efficiency (maximum quantum yield: F v /F m) showed a decline at 30°C than at 25°C in both clades. Symbiodinium clade C1 showed a consistently higher rETRmax with larger fluctuations than clade D, with a lower survival rate of juveniles during thermal stress treatment. Under strong light exposure, corals containing clade C1 showed a greater decline in F v /F m (-74%), compared to decline in corals associated with clade D (-50%) after 3 hours. This is the first study to assess stress tolerances of juvenile corals in association with the monoclonal Symbiodinium clades C and D, and our results indicated greater tolerance of corals associated with clade D to strong light (500 μmol m-2 s-1). However, it is difficult to determine the impact of high-temperature stress on coral-algae symbiosis from photosynthetic activity. At high temperatures, clade C1 Symbiodinium exhibited high photosynthetic activity, but host survival rates were higher in corals associated with clade D Symbiodinium. Since clade C1 has a relatively high photosynthetic activity under high temperatures, clade C1 symbiosis at high temperatures might have a negative impact on corals compared with clade D.

Heat Induction of Cyclic Electron Flow around Photosystem I in the Symbiotic Dinoflagellate Symbiodinium.

Increases in seawater temperature impair photosynthesis (photoinhibition) in the symbiotic dinoflagellate Symbiodinium within cnidarian hosts, such as corals and sea anemones, and may destroy their symbiotic relationship. Although the degree of photoinhibition in Symbiodinium under heat stress differs among strains, the differences in their responses to increased temperatures, including cyclic electron flow (CEF), which sustains photoprotective thermal energy dissipation, have not been investigated. Here, we examined CEF in cultured Symbiodinium cells or those in an endosymbiotic relationship within a cnidarian host. The light-dependent reduction of the primary electron donor photosystem I, i.e. P700(+), was enhanced in any Symbiodinium cell by increasing temperatures, indicating CEF was induced by heat, which was accompanied by thermal energy dissipation activation. The critical temperatures for inducing CEF were different among Symbiodinium strains. The clade A strains with greater susceptibility to photoinhibition, OTcH-1 and Y106, exhibited higher CEF activities under moderate heat stress than a more phototolerant clade B strain Mf1.05b, suggesting that the observed CEF induction was not a preventive measure but a stress response in Symbiodinium.

Transcriptomic characterization of the enzymatic antioxidants FeSOD, MnSOD, APX and KatG in the dinoflagellate genus Symbiodinium.

BackgroundThe diversity of the symbiotic dinoflagellate Symbiodinium sp., as assessed by genetic markers, is well established. To what extent this diversity is reflected on the amino acid level of functional genes such as enzymatic antioxidants that play an important role in thermal stress tolerance of the coral-Symbiodinium symbiosis is, however, unknown. Here we present a predicted structural analysis and phylogenetic characterization of the enzymatic antioxidant repertoire of the genus Symbiodinium. We also report gene expression and enzymatic activity under short-term thermal stress in Symbiodinium of the B1 genotype.ResultsBased on eight different ITS2 types, covering six clades, multiple protein isoforms for three of the four investigated antioxidants (ascorbate peroxidase [APX], catalase peroxidase [KatG], manganese superoxide dismutase [MnSOD]) are present in the genus Symbiodinium. Amino acid sequences of both SOD metalloforms (Fe/Mn), as well as KatG, exhibited a number of prokaryotic characteristics that were also supported by the protein phylogeny. In contrast to the bacterial form, KatG in Symbiodinium is characterized by extended functionally important loops and a shortened C-terminal domain. Intercladal sequence variations were found to be much higher in both peroxidases, compared to SODs. For APX, these variable residues involve binding sites for substrates and cofactors, and might therefore differentially affect the catalytic properties of this enzyme between clades. While expression of antioxidant genes was successfully measured in Symbiodinium B1, it was not possible to assess the link between gene expression and protein activity due to high variability in expression between replicates, and little response in their enzymatic activity over the three-day experimental period.ConclusionsThe genus Symbiodinium has a diverse enzymatic antioxidant repertoire that has similarities to prokaryotes, potentially as a result of horizontal gene transfer or events of secondary endosymbiosis. Different degrees of sequence evolution between SODs and peroxidases might be the result of potential selective pressure on the conserved molecular function of SODs as the first line of defence. In contrast, genetic redundancy of hydrogen peroxide scavenging enzymes might permit the observed variations in peroxidase sequences. Our data and successful measurement of antioxidant gene expression in Symbiodinium will serve as basis for further studies of coral health.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-015-0326-0) contains supplementary material, which is available to authorized users.

Low-Temperature Spectroscopic Properties of the Peridinin–Chlorophyll a–Protein (PCP) Complex from the Coral Symbiotic Dinoflagellate Symbiodinium

The spectroscopic properties of the peridinin-chlorophyll a-protein (PCP) from the coral symbiotic dinoflagellate Symbiodinium have been characterized by application of various ultrafast optical spectroscopies including femto- and nanosecond time-resolved absorption and picosecond time-resolved fluorescence (TRF) at 77 K. Excited state properties of peridinin and Chl a and their intramolecular interaction characteristics have been obtained from global fitting analysis and directed kinetic modeling of the data sets and compared to their counterparts known for the PCP from Amphidinium carterae. The lifetimes of the excited state of peridinin show close agreement with those known for the counterpart PCP, demonstrating that molecular interactions have the same characteristics in both complexes. More variances have been recorded for the excited state properties of Chl a including elongation of both the intramolecular energy transfer time between Chl's within the pair in the protein monomer and the excited state lifetime of the long wavelength form of Chl a (terminal acceptor). Kinetic modeling of formation of the peridinin triplet state has shown that the PCP is protected from potential photodamage due to an extremely fast peridinin triplet state formation of kTT = (14.4 ± 2.3) × 10(9) s(-1) ((70 ± 12)(-1) (ps)(-1)) that guarantees instantaneous depletion of Chl a triplets and prevents formation of harmful singlet oxygen ((1)ΔgO2).

Spectroscopic properties of the Chlorophyll a–Chlorophyll c 2–Peridinin-Protein-Complex (acpPC) from the coral symbiotic dinoflagellate Symbiodinium

Femtosecond time-resolved transient absorption spectroscopy was performed on the chlorophyll a-chlorophyll c 2-peridinin-protein-complex (acpPC), a major light-harvesting complex of the coral symbiotic dinoflagellate Symbiodinium. The measurements were carried out on the protein as well on the isolated pigments in the visible and the near-infrared region at 77 K. The data were globally fit to establish inter-pigment energy transfer paths within the scaffold of the complex. In addition, microsecond flash photolysis analysis was applied to reveal photoprotective capabilities of carotenoids (peridinin and diadinoxanthin) in the complex, especially the ability to quench chlorophyll a triplet states. The results demonstrate that the majority of carotenoids and other accessory light absorbers such as chlorophyll c 2 are very well suited to support chlorophyll a in light harvesting. However, their performance in photoprotection in the acpPC is questionable. This is unusual among carotenoid-containing light-harvesting proteins and may explain the low resistance of the acpPC complex against photoinduced damage under even moderate light conditions.

Influence of the Quantity and Quality of Light on Photosynthetic Periodicity in Coral Endosymbiotic Algae

Symbiotic corals, which are benthic organisms intimately linked with their environment, have evolved many ways to deal with fluctuations in the local marine environment. One possible coping mechanism is the endogenous circadian clock, which is characterized as free running, maintaining a ∼24 h periodicity of circuits under constant stimuli or in the absence of external cues. The quantity and quality of light were found to be the most influential factors governing the endogenous clock for plants and algae. Unicellular dinoflagellate algae are among the best examples of organisms that exhibit circadian clocks using light as the dominant signal. This study is the first to examine the effects of light intensity and quality on the rhythmicity of photosynthesis in the symbiotic dinoflagellate Symbiodinium sp., both as a free-living organism and in symbiosis with the coral Stylophora pistillata. Oxygen production measurements in Symbiodinium cultures exhibited rhythmicity with a periodicity of approximately 24 h under constant high light (LL), whereas under medium and low light, the cycle time increased. Exposing Symbiodinium cultures and corals to spectral light revealed different effects of blue and red light on the photosynthetic rhythm, specifically shortening or increasing the cycle time respectively. These findings suggest that the photosynthetic rhythm is entrained by different light cues, which are wired to an endogenous circadian clock. Furthermore, we provide evidence that mRNA expression was higher under blue light for two potential cryptochrome genes and higher under red light for a phytochrome gene isolated from Symbiodinium. These results offer the first evidence of the impact of the intensity and quality of light on the photosynthetic rhythm in algal cells living freely or as part of a symbiotic association. Our results indicate the presence of a circadian oscillator in Symbiodinium governing the photosynthetic apparatus through a light-induced signaling pathway that has yet to be described.

The photokinetics of thermo‐tolerance in Symbiodinium

AbstractThere is currently much debate about the ecological advantages for reef corals of hosting multiple types of the symbiotic dinoflagellate Symbiodinium. Amongst these is their apparent capacity to tolerate higher than normal water temperatures. There is strong photokinetic evidence that the trait of heat‐tolerance in plants is accompanied by energetic tradeoffs but little such evidence yet exists for corals. We use rapid light curves (RLCs) to investigate the photokinetic basis for thermo‐tolerance in the reef coral Acropora millepora with symbionts of contrasting thermal tolerance for which there are measured differences in energetics. Our results show that under non‐stressful temperatures, corals with heat‐tolerant type D Symbiodinium had a 41% lower maximum relative electron transport rate (rETRmax) and lower light absorption efficiency (α) due to lower cell Chl a content compared with corals with heat‐sensitive type C2 symbionts. Our results provide support for a photokinetic link between heat tolerance and deficits in holobiont (coral + symbiont) growth, lipid stores and reproduction. Reduced electron transport rate and light absorption capacity may be genotype‐specific attributes that enable clade D symbionts and their cnidarian hosts to cope with temperature stress but they inherently influence the photosynthetic function of the symbionts and thus have negative downstream effects on the coral.

Bioactive secondary metabolites from symbiotic marine dinoflagellates: symbiodinolide and durinskiols

Symbiotic relationships play critical roles in marine ecosystems. Among symbionts, marine dinoflagellates have attracted the attention of natural products chemists, biologists, and ecologists, since they are rich sources of unique bioactive secondary metabolites. The polyol compound symbiodinolide, which was isolated from the symbiotic dinoflagellate Symbiodinium sp., exhibits significant voltage-dependent N-type Ca(2+) channel-opening activity and may serve as a defense substance to prevent digestion of the host animals. Durinskiols are also unique long carbon-chain polyol compounds that were isolated from the dinoflagellate Durinskia sp. We found a selective cleavage reaction of allylic 1,2-diol using an olefin metathesis catalyst, and developed a fluorescent-labeling method for MS/MS analysis to achieve the structural elucidation of huge polyol compounds. This review highlights recent advances in structural and biological studies on symbiodinolide, durinskiols, and related polyol compounds.

Symbiospirols: Novel Long Carbon-Chain Compounds Isolated from Symbiotic Marine Dinoflagellate Symbiodinium sp.

Symbiospirols A, B, and C, long carbon-chain compounds with a molecular weight of 1207 were isolated from the cultured symbiotic dinoflagellate Symbiodinium sp. Their planar structures and partial relative stereochemistries were elucidated based on 1D and 2D NMR spectra and a degradation reaction. Symbiospirols consisted of a C67-linear chain with a beta,beta'-dihydroxyl ketone moiety, eight hydroxyl groups, one tetrahydropyran ring, and two 1,6-dioxaspiro[4,4]nonane rings. Symbiospirol A had an inhibitory effect against l-phosphatidylserine-induced PKC activation.

Symbiont acquisition strategy drives host–symbiont associations in the southern Great Barrier Reef

Coral larvae acquire populations of the symbiotic dinoflagellate Symbiodinium from the external environment (horizontal acquisition) or inherit their symbionts from the parent colony (maternal or vertical acquisition). The effect of the symbiont acquisition strategy on Symbiodinium-host associations has not been fully resolved. Previous studies have provided mixed results, probably due to factors such as low sample replication of Symbiodinium from a single coral host, biogeographic differences in Symbiodinium diversity, and the presence of some apparently host-specific symbiont lineages in coral with either symbiont acquisition strategies. This study set out to assess the effect of the symbiont acquisition strategy by sampling Symbiodinium from 10 coral species (five with a horizontal and five with a vertical symbiont acquisition strategy) across two adjacent reefs in the southern Great Barrier Reef. Symbiodinium diversity was assessed using single-stranded conformational polymorphism of partial nuclear large subunit rDNA and denaturing gradient gel electrophoresis of the internal transcribed spacer 2 region. The Symbiodinium population in hosts with a vertical symbiont acquisition strategy partitioned according to coral species, while hosts with a horizontal symbiont acquisition strategy shared a common symbiont type across the two reef environments. Comparative analysis of existing data from the southern Great Barrier Reef found that the majority of corals with a vertical symbiont acquisition strategy associated with distinct species- or genus-specific Symbiodinium lineages, but some could also associate with symbiont types that were more commonly found in hosts with a horizontal symbiont acquisition strategy.